1. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (1/18) A Polarity Checker for LHC Magnets L. Bottura, G. Brun, M. Buzio, G. Fievez, P. Galbraith, J. Garcia Perez, R. Lopez, A. Masi, S. Russenschuck, N. Smirnov, F. Thierry, A. Tikhov 1.Introduction 2.Measurement method 3.Hardware 4.Software 5.Characterization 6.Test results 7.Conclusions and outlook Contents Ref: M Buzio et al, “Checking the Polarity of Superconducting Multipole LHC Magnets”, paper presented at MT-19

2. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (2/18)  the LHC will include about 1750 cryomagnet assemblies, up to almost 16 m long, housing a total of about 10000 superconducting magnets connected in 1612 electrical circuits  magnet connection errors are always detrimental and may be unacceptable in some cases, including esp. main dipoles and quadrupoles, insertion region magnets, skew and tuning quadrupole correctors  need to check systematically multipole order, type and polarity of all LHC magnetic elements  automated, self-contained probe based on a rotating Hall sensor designed and built  similar system used with success at BNL for RHIC and presented at IMMW XI, Brookhaven (A. Jain et al.) 1.1 – Introduction: Purpose of the system 1232 cryodipoles, including 3696 corrector spool pieces 360 arc Short Straight Sections, divided in 61 sub-types including 260 main quadrupoles and 1080 corrector magnets ~8000 total superconducting corrector magnets 106 Short Straight Sections for the insertion regions

3. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (3/18) Specifications: - general-purpose system for any multipole order and type (normal or skew) - automatic, self-contained, fast - room temperature measurements, fit inside beam pipe (Ø 50 mm) - minimum field 60  T (~earth field !) 1.2 – Introduction: Specifications Magnet Type T.F. [mT/A] I max [A] B max [mT] Diode Main Dipole (MB)0.665.03.32 Y B1 arc Orbit Corrector (MCBV/H)52.700.12.64 B1 IR Orbit Corrector (MCBXH/V)6.092.414.62 Main Quadrupole (MQ)0.293.00.88 Y Tuning Quadrupole (MQT)0.103.00.31 B3 Multipole Corrector (MCS)0.053.00.15 Y B3 Lattice Corrector (MS)0.023.00.07 B4 Multipole Corrector (MCO)0.403.01.20 Y B4 Lattice Corrector (MO)0.561.00.56 B5 Multipole Corrector (MCD)0.183.00.55 Y B6 Multipole Corrector (MCTX)0.130.50.06

4. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (4/18)  Radial component (normal to Hall sensor)  Vector of N values sampled at regular intervals  DFT of the radial field vector  Inverse DFT of the radial field vector 2.1 – Measurement method: Harmonic analysis of radial field Harmonic field coefficients as a function of the DFT of sampled values * denotes complex conjugation expand, equate term by term

5. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (5/18) 2.2 – Measurement method: Transfer function Magnets without diode installed Magnets with diode installed  For greater accuracy, polarity is determined on the basis of (approximate) transfer function rather than raw harmonic measurement  An arbitrary number of current points can be specified; minimum is two, of opposite sign if possible  Linear best fit to {C n,I} pairs CnCn I I1I1 I2I2 CnCn I I1I1 I2I2 Transfer function [T/A @ 17 mm] Remanent field [T @ 17 mm] (+ Hall voltage offset)

6. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (6/18) 3.1 – Hardware: Probe (“mouse”) ParameterValue Probe length (mm)768 Probe external diameter (mm)  40 Tube internal diameter (mm)  40 to  73 Tilt sensor range  45° Tilt sensor resolution (mrad)0.1 Hall plate current (mA)50 Hall plate sensitivity (mV/T)233.8 Hall plate radius (mm)11 Hall plate azimuthal offset (mrad)10.5 Hall plate max. field (mT)30 Hall plate min. field (mT)0.01 On-board Preamplifier gain500 Azimuthal resolution (mrad)0.047 Functional block diagram  4+1 units in operation at CERN  24x256-stage stepping motor with 22:1 reduction gearbox  electrolytic tilt sensor  longitudinal transport motor not in use (manual positioning)

7. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (7/18) 3.2 – Hardware: DAQ system Mobile rack Power supplies for rack, DC motor, tilt sensor, stepping motor Voltmeter (tilt sensor) 50 mA Hall supply Windows PC (+ DAC for Hall output acquisition) Keithley 2001 multiplexer DAQ electronics rack Bipolar Kepco magnet power supply Custom data switching unit

8. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (8/18) 3.3 – Hardware: Connections to main cryoassemblies  standardized connections to cryodipoles and arc Short Straight Sections allow fully automatic sequential powering of the magnets  connections to magnets for the Insertion Regions are done manually (106 cryoassemblies, 16 types) cryodipole short straight section

9. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (9/18) User panel, wizard-style interface 4.1 – Software: LabView user interface On-line assessment of results by cross-checking with expected values Automatic generation of pdf test report Manual input of assembly/magnets to be tested

10. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (10/18) 4.2 – Software: Configuration files (examples) Magnet definition file

11. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (11/18) Assembly configuration file 4.3 – Software: Configuration files (examples) Magnet configuration file Expressed in the magnetic measurement reference frame (…) 4 types of cryodipoles, 61 + 16 types of short straight section in the arcs and insertions

12. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (12/18) The calibration of the probe concerns mainly two parameters:  Voltage-to-field transfer function of the Hall plate + preamplifier combination (~8.5 mT/V): determined by measuring the loadline of a reference dipole and cross-checking with a Metrolab NMR teslameter  Angular offset between Hall plate and tilt sensor (~10 mrad): determined as the average of the field direction obtained from two harmonic measurements in a reference dipole, inserting the probe from both ends. Other systematic and random factors affecting the measurement that were neglected include: - roll/pitch angle error of the Hall plate (  pick-up of tangential/longitudinal field component) - error  R in the radial position R of the Hall plate (  error (n-1)  R/R in the field coefficients) - planar effect - temperature drift 5.1 – Characterization: Calibration linearity error of the Hall sensor: <3% for all cases of interest

13. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (13/18) 5.2 – Characterization: Validation (1) results were consistent in both cases The polarity of Hall sensor output was verified with two methods: 1) deformation of current-carrying wire from right-hand rule: F = I × B 2) commercial 3D Hall probe teslameter (Metrolab THM7025) N S B magnetic field force current + -

14. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (14/18) 5.3 – Characterization: Validation (2) A systematic verification procedure was carried out on magnets of order n=1 to 5 (total = 5x4x2 measurements): 1) Install magnet so that field is normal positive 2) Check polarity with commercial Hall teslameter 3) Verify multipole order, magnet type and polarity with the Polarity Checker in four cases: {  current, insertion from connection or non-connection end} polarity must reverse with the current (always) and with insertion side (only n=2,4) 4) Turn magnet by -  /n to make it skew, repeat step 3) e.g. Normal negative quadrupole results were conforming to expectations in all cases expected B r ( ) measured B r ( )

15. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (15/18) 5.4 – Characterization: Repeatability tests repeatability of the main field: better than ~1% in all tested cases repeatability of field direction: between 2 and 8 mrad The repeatability of the system was checked by running 60 consecutive measurements in the reference magnets. affected by errors in the dynamic readout of the electrolytic tilt sensor + feed-forward control of the stepper motor

16. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (16/18) 5.5 – Characterization: Overall performance Quantity Estimated accuracy Unit Main field amplitude5%mT Main field direction 33 deg Main harmonic ordererror-free Main harmonic polarityerror-free Main harmonic typeerror-free  main field accuracy: depends on repeatability + linearity error  field direction accuracy: depends on repeatability + main field error  time required for - single acquisition: 0.75 s (motor must be switched off) - harmonic measurement: 90 s - full standard cryomagnet: ~1 hour 10% rejection threshold on the difference between measured and expected T.F. inadequate for field direction measurements main field accuracy << amplitude of other harmonic components field direction accuracy << threshold to discriminate phase of main component (worst case=dodecapole=15°) no errors reasonably expected for the target measurement results

17. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (17/18) 6 – Test results: Summary of results of first 505 cryoassemblies 1% of faults in cryodipoles, 20% in Short Straight Sections non-critical errors, all easily rectified at CERN

18. L Bottura, M Buzio, JG Perez, A Masi, N Smirnov, A Tikhov, et al., “A Polarity Checker for LHC Magnets” IMMW 2005, 14th International Magnetic Measurement Workshop, CERN, 26-29 September 2005 (18/18) 7 – Conclusions and outlook 4 units built and in use at CERN, proved reliable and easy to use 505 cryoassemblies tested, 1200 to go before end 2006 Automated test procedures for cryodipoles and short straight sections fully established: inner-region insertion quadrupoles/correctors being finalized now Possible further developments (not really necessary for series tests) include: - improving the mechanics of the longitudinal transport system - characterization of neglected error sources